The present invention relates generally to orthopaedic surgery and in particular to shoulder prostheses. More particularly, the present invention relates to a rotatable collar forming part of a humeral prosthesis. Alternatively, the rotatable collar may form part of a femoral prosthesis. The present invention also relates to an assembled prosthesis and a surgical shoulder arthroplasty procedure using the humeral prosthesis.
A natural shoulder joint may undergo degenerative changes for a variety of reasons, for instance arthritis. Alternatively, a shoulder joint may be fractured or otherwise damaged by an external force. When a shoulder joint is sufficiently degenerated or damaged it may be necessary to replace a natural shoulder with a prosthetic shoulder joint. Conventional shoulder prostheses comprise a humeral prosthesis, optionally with a glenoid prosthesis. For total or reverse arthroplasty a glenoid component is implanted, however for hemi arthroplasty the humeral component articulates against the natural glenoid cavity.
Typically, the humeral component comprises a stem for insertion into a bore extending into the intramedullary canal generally along the longitudinal axis of the bone and an articulation component, which may be a convex bearing head in the case of total arthroplasty or a concave cup in the case of reverse arthroplasty. Typically, the articulation component is coupled to a neck portion of the stem, which extends from the intramedullary canal at an inclined angle relative to the longitudinal axis of a distal portion of the stem in order to recreate the arrangement of the natural joint.
When the upper extremity of the humerus is fractured, the humerus generally breaks into several pieces, typically three or four. In particular, for “four part fractures” the humeral head splits off at the level of the anatomical neck, the greater and lesser tuberosities are separated from the humerus shaft below the tuberosities and the tuberosities are separated from one another along the bicipetal groove. As there is no longer a blood supply to the humeral head necrosis may begin. For repair of a four part fracture, the humeral head is replaced, and the greater and lesser tuberosities are reattached to the humeral shaft. Known shoulder prostheses for repair of a four part fracture provide tabs or fins attached to the stem which incorporate holes to receive sutures to couple the tuberosities and soft tissue such as tendons to the prosthesis. Correct positioning of the suture holes is essential to accommodate the differing attachment point of soft tissues to the humerus in a natural joint. For instance, U.S. Pat. No. 6,398,812 discloses a shoulder prosthesis with anatomic reattachment features for tendon or bone in which at least one set of tendon or bone reattachment features are provided along a line which is divergent with respect to the axis of the stem. This provides for reattachment of tendons, such as the supraspinatus tendon, which naturally lie along the top surface of the humerus.
US-2005/0177241 discloses an alternative humeral prosthesis in which a stem is anchored in the intramedullary canal and a metaphyseal portion extends upwardly from the stem and is joined to a flange supporting a prosthetic head. The primary purpose of the flange is to transfer force to the humeral shaft. The flange includes suture holes, for instance on its upper extremity, for suturing the tuberosities and soft tissue to the humeral prosthesis.
US-2007/0173945 discloses an implant system for total or hemi shoulder arthroplasties comprising a humeral stem having an enlarged head portion to receive modular interchangeable components, such as articulating liners, spacers and adapter inserts. The head comprises an annular outer rim incorporating a plurality of suture holes for reconstructing the proximal humerus for the repair of humeral fractures.
While it is known, for instance in the above discussed patent publications, to provide suitable attachment points for coupling bone fragments and soft tissue to a prosthesis implanted into the end of a long bone, known prostheses suffer from inflexibility in the position of attachment points which may result in loss of mobility for the repaired joint. It is an object of embodiments of the present invention to obviate or mitigate one or more of the problems of the prior art, whether identified herein or elsewhere.